Biogen (BIIB) stock split history
Biogen has split its stock twice since 1999. The latest was a 3-for-1 split on 18 Jan 2001: each share held before became 3 shares. Our price history does not reach back to that date, so we show no closing prices around it. Below: every split, what it did to the share count, and the chart with splits marked.
All BIIB stock splits
| Effective date | Split | Close before | First close after | Shares today per 1 held before |
|---|---|---|---|---|
| 18 Jan 2001 | 3-for-1 | – | – | 3 |
| 21 Dec 1999 | 2-for-1 | – | – | 6 |
Split is new shares for old shares: in a 10-for-1 split one share becomes ten. Close before is the last close before the effective date and first close after is the first close on or after it, both as traded in BIIB's own history (not adjusted), so the two differ by about the split ratio plus that day's market move. Shares today shows how many shares one share held just before that split has become after it and every later split. Dates and ratios: EODHD.
BIIB price chart with splits marked
The chart shows split-adjusted prices, so the price does not jump on a split date; each split is marked on the date axis. Use the buttons to change the range.
How to read BIIB's split history
A stock split changes the number of shares and the price per share by the same factor, so the value of a holding stays the same on the day. Biogen's 3-for-1 split on 18 Jan 2001 is the latest in our data: each share held before became 3 shares. Across all 2 splits since 1999, one share held just before the first split has become 6 shares.
A split does not change what a company earns or what it is worth. Per-share figures such as earnings and dividends per share are restated by the ratio, which is why old prices look different in an adjusted chart than in the newspaper of the day. The BIIB stock page has the current score and fair value range, and the BIIB price history lists daily prices with both as-traded and adjusted closes.
Recent splits in the same sector: Health Care
| Company | Latest split | Date |
|---|---|---|
| COO Cooper Companies | 4-for-1 | 20 Feb 2024 |
| TECH BIO-TECHNE | 4-for-1 | 30 Nov 2022 |
| DXCM Dexcom | 4-for-1 | 13 Jun 2022 |
| ISRG Intuitive Surgical | 3-for-1 | 5 Oct 2021 |
| EW Edwards Lifesciences | 3-for-1 | 1 Jun 2020 |
| CNC Centene | 2-for-1 | 7 Feb 2019 |
| HSIC Henry Schein | 2-for-1 | 15 Sep 2017 |
| IDXX Idexx Laboratories | 2-for-1 | 16 Jun 2015 |
Frequently asked questions
When did Biogen last split its stock?
The last BIIB stock split in our data took effect on 18 Jan 2001. It was a 3-for-1 split: each share held before became 3 shares. Our price history does not reach back to that date, so we show no closing prices around it.
How many times has Biogen split its stock?
Biogen (BIIB) has had 2 stock splits since 21 Dec 1999 in our data, which goes back to 1990. Taken together, one share held just before the first split has become 6 shares.
Has Biogen announced a new stock split?
Our data lists no split for BIIB after 18 Jan 2001 and no announced future one as of 22 Oct 2026. A company announces a split first, usually together with earnings or in a filing, and the split takes effect weeks later. The company's 8-K filings and press releases are the primary source.
What does a 3-for-1 split mean for shareholders?
In a 3-for-1 split the number of shares goes up and the price per share goes down by the same factor: each share held before became 3 shares. The total value of a holding is not changed by the split itself; it only changes with the market price afterwards.
Does a stock split change what a company is worth?
No. A split cuts the same company into more (or fewer) pieces, so market value, earnings and dividends per share are all restated by the ratio. Charts and per-share figures in our data are adjusted for splits so that past and present prices can be compared.
Where does this split data come from?
Split dates and ratios come from EODHD. The closing prices around each split are the as-traded closes in our database. Feed entries that are only price-adjustment factors for spin-offs or special distributions are not counted as splits.
Related
Educational information, not financial advice. Split data to 22 Oct 2026; a company can announce a split at any time.